This article is about the first apple ii machine language book pdf-produced Apple computer. American households rather than businessmen or computer hobbyists. 1977 Trinity” of personal computing. Apple’s corporate logo until early 1998.
To me, a personal computer should be small, reliable, convenient to use and inexpensive”. The Apple II used a multiplicity of idiosyncratic engineering shortcuts to save hardware and reduce costs. Taking advantage of the way that 6502 processor only accesses memory on alternate phases of the clock cycle, the video generation circuitry’s memory access on the otherwise unused phase avoids memory contention issues and interruptions of the video stream. Wozniak used a simple timer circuit whose period is proportional to the resistance of the game controller, and used a software loop to measure the timer. A single 7 MHz master oscillator was divided by various ratios to produce all other required frequencies, including the microprocessor clock signals, the video transfer counters, and the color-burst samples. Similarly, in the high-resolution graphics mode, color is determined by pixel position and can thus be implemented in software, saving Wozniak the chips needed to convert bit patterns to colors.
The Disk II interface, created by Wozniak, is regarded as an engineering masterpiece for its economy of electronic components. The approach taken in the Disk II controller is typical of Wozniak’s designs. The cost of such terminals could easily exceed the price of the computer itself. The Apple II’s PCB underwent several revisions as Steve Wozniak made modifications to it. The earliest version was known as Revision 0, and the first 6,000 units shipped used it. Revision 0 Apple IIs powered up in an undefined mode and had garbage on-screen, requiring the user to press Reset.
This was eliminated on the later board revisions. Revision 0 Apple IIs could display only four colors, but Wozniak was later able to generate 16 in low-res mode. DRAM and had jumper switches to adjust the RAM size. DRAM prices, Apple redesigned the circuit boards without the jumpers so that only 16k chips were supported. A few months later they started shipping all machines with a full 48 KB complement of DRAM.
The original NTSC television signal specification was black-and-white. Color was added on later by adding a 3. 58-MHz subcarrier signal that was partially ignored by black-and-white TV sets. The result is that the position, size, and intensity of a series of pulses define color information. The Apple II display provides two pixels per subcarrier cycle. When the color burst reference signal is turned on and the computer attached to a color display, it can display green by showing one alternating pattern of pixels, magenta with an opposite pattern of alternating pixels, and white by placing two pixels next to each other. Blue and orange are available by tweaking the offset of the pixels by half a pixel-width in relation to the color-burst signal.
The coarse, low-resolution graphics display mode works differently, as it can output a pattern of dots per pixel to offer more color options. These patterns are stored in the character generator ROM and replace the text character bit patterns when the computer is switched to low-res graphics mode. The text mode and low-res graphics mode use the same memory region and the same circuitry is used for both. Written by Wozniak, the interpreter enabled users to write software applications without needing to purchase additional development utilities. Written with game programmers and hobbyists in mind, the language only supported the encoding of numbers in 16-bit integer format. 32767 reduced the machine’s attractiveness to business users. Jobs responded by licensing a floating-point version of BASIC from Microsoft which was initially available as a plug-in expansion card.
Models with Applesoft BASIC in ROM and the optional “Language Card” installed could load Integer BASIC from disk if needed. This feature enabled hackers to write and debug machine code programs without needing further development software. The Z80 card also allows the connection to a modem and thereby to any networks that the user might have access to. In the early days, these were scarce, but expanded significantly with the development of bulletin board systems. Level One to be run. But the company also had “to negotiate the attitudes of its potential buyers, bearing in mind social anxieties about the uptake of new technologies in multiple contexts. The office, the home and the ‘office-in-the-home’ were implicated in these changing spheres of gender stereotypes and technological development.